KR100436861B1 - Method and apparatus for inspecting defects on polishing pad to be used with chemical mechanical polishing apparatus - Google Patents

Abstract

The present invention provides an apparatus and method for detecting defects created in a polishing pad for chemically and mechanically polishing a wafer. The defect detection apparatus includes a pad driving device for mounting and moving a pad, a camera installed toward the pad and outputting an image of the pad as an electrical signal, and digital image data acquisition for converting an electrical signal transmitted from the camera into a digital signal. And an image data processing unit for processing the image data to detect defects.

Description

TECHNICAL MECHANICAL POLISHING PAD TO METHOD AND DEVICE OF DEFINITION OF POLICY PAD

The present invention relates to an apparatus and method for inspecting defects in a polishing pad for use in a polishing apparatus for chemically and mechanically polishing a wafer.

In the semiconductor process, the surface is sometimes uneven after applying the necessary thin film to the wafer. If the flatness is degraded, accurate circuit patterns cannot be obtained in subsequent photographic processes. In view of these problems, the uneven surface is polished. The waiter is pressed and rotated on the polishing pad while spraying a suspension called a slurry containing inorganic particles and a surfactant on the polishing pad. The mechanical friction between the wafer and the suspension and the chemical dissolution of the suspension then combine to smoothly polish the surface of the wafer. This process is called chemical mechanical polishing (CMP).

In recent years, the line width of semiconductor devices has been rapidly reduced, and the process tolerances allowed in the photolithography process are rapidly decreasing. For this reason, the necessity of this chemical mechanical polishing greatly increased. Most domestic and foreign state-of-the-art semiconductor factories have introduced dozens of grinding machines per plant.

One problem of this process is that surface scratches occur during polishing. Severe scratching of the surface can damage the circuitry and cause the wafer to be discarded. Even minute scratches reduce the efficiency of the photographic process, resulting in lower overall yield.

There are many reasons for such scratches. If the slurry contains too large particles in the inorganic particles, scratching occurs. Aggregation of particles in the slurry during polishing may occur. Particles from outside can fall on the pads and become a problem For example, metal particles may fall from a part in the polishing apparatus. Also problematic are diamond particles that fall during diamond pad conditioning, which are used for a period of time and performed to improve the condition of the pad. Further, there is a problem when the particles are separated on the polishing pad before the polishing operation, or when the particles are contained in the polishing pad and protrude during use.

Problems arising from the slurry have been greatly improved by inspecting various measuring equipment and filtering them using a filter or the like. Problems caused by diamond pad conditioners have also been almost eliminated due to the quality improvement efforts of diamond pad conditioners. However, there is still not enough inspection or treatment for defects in the polishing pad itself.

In view of the above problems of the prior art, the present invention provides an apparatus and method for inspecting a polishing pad for chemical mechanical polishing of a wafer. By inspecting the defects on the polishing pad, you can ultimately protect the wafer.

Figure 1 (a) is a perspective view of the polishing pad, (b) is a partial cross-sectional view showing the surface of the polishing pad.

Figure 2 is a perspective view of the polishing pad defect inspection apparatus according to an embodiment of the present invention

Figure 3 is a perspective view of the case removed to reveal the interior of the device shown in Figure 2

Figure 4 is a system configuration of the polishing pad defect inspection apparatus according to an embodiment of the present invention

5 is a bottom view of the lighting apparatus provided in the apparatus shown in FIG.

Fig. 6 is a longitudinal sectional view of the lighting apparatus of Fig. 5, (a) is a longitudinal sectional view of a lighting unit for black and white photographing of the lighting device, and (b) is a longitudinal sectional view of a lighting unit for color photographing of the lighting device.

7 is a flowchart illustrating a process of scanning for defect inspection

8 and 9 are diagrams for visually understanding the results of processing data to detect particles.

* Explanation of symbols for main parts of the drawings

100: defect inspection device 110: turntable 112: linear movement device

114: monochrome line scanning camera 116: color line scanning camera

118: lighting device 140: central control unit

The present invention detects particles (particles) originally attached to the pads, particles or other pad defects contained therein, to prevent the problem pads from being used in the device, and is used when scratches occur on the wafer. The present invention provides a device for inspecting a used pad and detecting a defect causing the scratch. The basic method of detecting defects by processing image data in the present invention is to analyze whether values such as the gray scale of each pixel in the pad image appear to be sharply different from the surroundings.

By eliminating the pad defect, there is an advantage that the process defects that may be caused by the pad is blocked in advance, and the cause of the defect that has already occurred can be found to obtain a direction for improving the process later. In addition, the present invention, after the detection of the defect by distinguishing the image by the image and its size and type of the defect statistical processing, the user can identify the tendency of the polishing pad in the short or long term, the association with the process, the correlation with the yield, etc. Can be identified.

According to one aspect of the invention, for detecting defects generated in the polishing pad for chemically and mechanically polishing the wafer,

A pad driving device for mounting and moving the pad,

A camera installed toward the pad and outputting an image of the pad as an electric signal;

A digital image data acquisition device for converting an electrical signal transmitted from the camera into a digital signal;

A defect detection apparatus for a polishing pad is provided that includes an image data processing unit that processes the image data transferred from the digital image data acquisition device to detect a defect.

In a preferred embodiment the camera is a line camera with a monochrome or color line CCD extending radially. The pad drive includes a turntable that rotates about the center of the pad with a central axis. In particular, the longitudinal direction of the line CCD of the line camera is arranged to coincide with the radial direction of the pad.

The detection device further comprises an illumination device facing the surface of the pad. The lighting apparatus includes a support having a slit extending radially of the pad, and a light emitting device extending along the slit and installed toward the pad around the slit.

The image data processing unit obtains one or two or more values of the quantitative characteristic values of light obtained from the image data for any one point of the image data of the pad obtained by the image data acquisition device, and obtains the obtained quantitative characteristic values. When a level value obtained from any one or a combination of two or more of the level value obtained from the image data around the point of the pad appears by more than a predetermined amount, the point at which the difference appears is determined as a defect. In processing the data of any one point on the pad, the average value of the level value for the points in the adjacent position of the point is obtained, and the average level value is subtracted from the level value for the one point, and the like. Eliminate the effects of

The pad drive includes a turntable that rotates about the center of the pad as a center axis, and synchronizes a pulse signal corresponding to a rotation of a predetermined angle of the turntable with a trigger signal of the image data acquisition device.

According to another aspect of the invention, for detecting defects generated in the polishing pad for chemically and mechanically polishing the wafer,

Rotating the polishing pad about its center;

Acquiring a linear image extending radially of the polishing pad on the polishing pad;

Converting the image into an electrical signal;

Converting the electrical signal into digital image data;

A defect detection method of a polishing pad is provided that includes processing the digital image data.

According to another aspect of the present invention, a program executed by an image data processing processor provided for processing image data, the quantitative characteristic values of light obtained from the image data for any one point of the image data of the polishing pad And a level value obtained from any one or a combination of two or more of the obtained quantitative characteristic values to obtain a difference between level values obtained from image data around the point of the polishing pad, and the difference is A computer readable recording medium is provided which contains a program for comparing the difference over a preset amount.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

1, a polishing pad 10 is shown. Referring to Fig. 1A, the polishing pad 10 is disc shaped. The diameter is generally about 50 cm, but the present invention is not limited thereto. The polishing pad 10 is made of a resin material such as polyurethane, for example. Referring to FIGS. 1A and 1B, the polishing pad surface 11 has a plurality of concentric grooves (herein referred to herein as “grooves” or “golves”) 12. Is formed from the center to the rim. This groove 12 is for inflow and outflow of the slurry. The bone is concentrically shaped from the center of the pad. Although not shown in detail, extremely fine small grooves called pores (not shown) are formed on the surface of the polishing pad, so that the structure is like a sponge. This pore is intended to improve polishing performance.

Referring to (b) of FIG. 1, the term 'defect' may be used to describe defects occurring on the pad surface 11 (the defects inherent in the concept of particles). There are several). Particle 14, spot 16, red spot, hole 18, bridge 20 and the like. Automatic classification of these defects is based on the color and shape characteristics of the defect. Each type of defect has its own color and shape characteristics. Color characteristic detection is to find other features compared to normal pad surface color. Morphological detection involves finding features such as defect size and appearance. A weight is assigned to each characteristic, and the characteristics are determined to determine the type of defect. Each defect is explained in full detail.

Particles

Particle 14, one of the defects, refers to this material that has fallen on the surface 11 of the polishing pad 10 from the outside. As a rule, it has a distinctly dark color (black) compared to the normal pad surface 11. In addition, the color change with the normal pad surface 11 is sharp. The size is relatively small, and the size is about 50 μm to 200 μm. These particles have the following characteristics.

-HSI model analysis: Because the particles are black, the intensity (also called intensity, luminous intensity, and brightness) drops sharply.

RGB model analysis: Particles are black while the normal pad surface is off-white. Off-white has a high level of red (also known as R level), slightly lower green level (also known as G level), and blue level (also called B level). Has a relatively low value. On the other hand, black is a value close to 0 in all of the R, G, and B levels. Therefore, the R level gap between the normal pad surface and the particle is the largest, the next G level gap is slightly larger, and in the case of the B level, the difference is not large compared to the R level or the G level.

The basic method of classifying a defect of a pad into particles is as follows. The average intensity value (I _pad ) of the _pad surface is obtained, and the average intensity value (I _defect ) of the _defect is obtained. If the difference between the I _pad and the I _defect value is a certain value (A) or more, the particles are classified.

2. Spot

Spot refers to a defect caused by the inclusion of foreign matter contained in the manufacturing process of the pad. The spots have a color that is similar to the normal pad surface or that is relatively less dark. The color change with the normal pad surface is slow. It is relatively large in size and is about 300 µm to 2500 µm. This spot has the following characteristics.

-HSI model analysis: Since the color difference from the normal pad surface is not large, the spot Hue (also known as Hue, Color, Hue) does not have a large difference from the Hue value of the normal pad surface. The intensity of the spot has a relatively lower value than the normal pad surface. Intensity changes are modest.

The basic method of classifying a defect in a pad as a spot is as follows. I _pad and I is the difference between the _defect value or less be regarded as defective are jeongdoyi predetermined value (B), an average Hue (Hue) value (H _pad) and an average Hue (Hue) value for the defect of the top pad surface (H _defect) If the difference is enough to be regarded as a defect, but below a certain value, it is regarded as a spot.

3. Red spot

The red spot is also a defect caused by the foreign matter contained in the pad manufacturing process and indicates that the spot is relatively red. Although there is no significant difference in the technical sense from the general spot described above, the general spot is red compared to the gray color, and the occurrence frequency of the spot is high. The color is similar to the normal pad surface and it is relatively reddish. The color change with the normal pad surface is slow. The size is relatively large, about 300 μm to 2500 μm, and the size is also wide. This red spot has the following characteristics.

-HSI model analysis: similar to spot. Hue value is relatively close to Red.

-RGB model analysis: Red spot is a relatively red spot with R level higher than G level and B level. Compared to the normal pad surface, the R level is higher than or similar to the R level of the normal pad surface. On the other hand, the G and B levels are lower than the G and B level values of the normal pad surface.

The basic method of classifying a pad defect as a red spot is as follows. And I _pad and I _defect value is less than chayiyi being a predetermined value enough to be recognized as a defect (C), the average Hue (Hue) value (H _pad) and Hue (Hue) value (H _defect) of the defects of the top pad surface If the difference is considered to be a defect but is below a certain value and the Hue value of the defect is close to the Red direction, it is regarded as a red spot.

4. Hole

It refers to a round semicircular hole formed on the surface of a normal pad, which is usually produced during pad manufacturing. The color is the same as the pad surface, but only the brightness changes dark. In particular, it darkens inward from the edge of the hole. The slope of the change in brightness is steep from the outside, but there is little change in brightness inside. The size is relatively large, about 500 ~ 1500㎛. These holes have the following characteristics.

-HSI model analysis: Hue values are almost the same as the normal pad surface, and the pixels that make up the hole have a uniformly low intensity value.

Therefore, if the brightness is different from the normal pad surface by a certain value or more, it is classified as a hole.

5. Bridge

It indicates a defect in which grooves (bones) generated in the manufacturing process of the pad are blocked. The bridge is a pad-like material. The color is halfway between the surface of the pad and the color of the bone. This defect is formed along the valley. The characteristics of the bridge are as follows.

-HSI model analysis: Hue values are almost the same as the normal pad surface, and the pixels that make up the bridge are slightly lower in intensity evenly.

The bridge has a value between the Hue value of the normal pad surface and the Hue value of the valley, so when such a value appears at the position of the groove (groove) in the scanning direction (circumferential direction), it is regarded as a bridge defect. Recognize.

When detecting and classifying the defect according to the present invention, it is preferable to go through the following process. The data obtained from the first black and white line scan camera are analyzed first to detect defects. In other words, the position where the gray scale value is obtained from the black and white image data and compared with the surroundings is recognized as a defective position. In the case of a defect that was recognized as a defect in the first stage but whose type is not clearly classified in the first stage, the defect is classified secondly from the color image data about the defect and its surroundings. The types of defects are screened based on the characteristics of each defect as described above using these HSI values. In the case of ordinary particles, remove them by blowing compressed air. If it is a problem such as a spot generated during the pad manufacturing process and defects are difficult to remove, the defect classification data is used as a basis for returning the polishing pad.

2 and 3, a defect inspection apparatus 100 according to an embodiment of the present invention includes a bed 102, a support 104 fixed on the bed, and a case 106 covering a portion of the support 104. And a support 108 provided in front of the case 106. 3 shows that the case 106 is removed and the inside is visible. The bed 102 is provided with various circuit devices to be described later, and a linear moving device 112 for linearly moving the turntable 110 and the turntable 110. The polishing pad 10 to be inspected is placed on the turntable 110. The support 104 is installed in one of the beds in a vertical direction, and the support 104 is provided with a black and white line scanning camera 114 and a color line scanning camera 116 facing the pad located below. In addition, the support 104 is provided with an illumination device 118 under the cameras 114 and 116. The display device 120 is installed in the case 106. Above the base 108 are input devices such as a keyboard 122 and a point input device 124.

2 to 4, the turntable 110 is for mounting the pad 10 thereon and rotating it. The turntable 110 is configured to install the pad 10 so that the center of the pad 10 coincides with the rotation center of the turntable 110. As one example, the turntable 110 is provided with a vacuum adsorption device and the pad is adsorbed. The turntable 110 includes a rotation drive motor 126 and a rotary encoder 128. As the drive motor 126, a precise stepping motor is preferable. A precision stepping motor, for example, is known as a micro step motor, and is designed to divide the basic step pulses 125 times again to generate up to 3.25 million pulses in one revolution. This is about 0.46㎛ the length of one step at the outermost of the pad, it can be seen that it is possible to control very precisely considering that the minimum size of one pixel to hold the camera of this equipment is 15㎛. For example, the model number VEXTA Step PK599BW of Oriental Motor of Tokyo, Japan can be used for the precision step motor used when constructing the turntable 110 for precisely rotating the pad 10. Model number DFU1514W from the same company can be used as the motor drive. Although not shown in detail, it is preferable that the turntable 110 includes a vacuum suction fixture for fixing the pad 10.

2 to 4, the linear movement device 112 is for moving the turntable 110 in a straight line from the loading position shown in FIG. 2 to the inspection position shown in FIG. In addition, at the inspection position, the linear movement device 112 can move the turntable 110 to a constant pitch (less than or equal to the radius of the pad). The linear movement unit 112 may be a linear motor. Usually, it can be composed of a rotation drive motor 113 and a linear conversion mechanism that is a precise stepping motor.

3 and 4, a B / W Linescan Camera 114 is installed on the support 104. The black and white line scanning camera 114 is installed to face the pad 10 when the pad 10 is in the inspection position, that is, face down vertically. The black and white line scanning camera 114 has a line CCD therein. This line CCD transfers the transmitted light to an electric control part which changes an electrical signal later. The longitudinal direction of the line CCD is provided so as to coincide with the radial direction of the pad at the inspection position. In addition, if the trajectory of the center of the pad 10 is moved as the moving axis when the pad 10 is transferred by the linear movement unit 112 by a constant pitch at the inspection position, the length of the line CCD is defined. Direction is parallel to the axis of movement. An example of such a monochrome line scanning camera 114 is Dalsa SP-12-02K40 of DALSA INC. (Homepage address www.dalsa.com) of Ontario, Canada.

3 and 4, a color line scanning camera 116 is installed on the support 104, which is installed next to the black and white line scanning camera 114. As shown in FIG. The color line scanning camera 116 is installed in the same manner as the black and white line scanning camera 114 so that when the pad 10 is in the inspection position, the pad 10 faces the pad 10, that is, vertically downward. The color line scanning camera 116 has a color line CCD therein. The color line CCD converts the transmitted light into an electric signal to be described later. Similarly to the black and white line scanning camera 114, the color line scanning camera 116 is installed so that the longitudinal direction of the color line CCD coincides with the radial direction of the pad at the inspection position. In addition, when the pad 10 is conveyed by a constant pitch by the linear transfer device 112 at the inspection position, the longitudinal direction of the line CCD is parallel to the movement axis of the pad. In the embodiment of the present invention, the longitudinal axis of the monochrome line CCD and the color line CCD and the movement axis of the pad are positioned on one plane extending in the vertical direction. An example of the color line scanning camera 116 is JAI CV-L103 of JAI, Yokohama, Japan.

The black and white line scanning camera 114 and the color line scanning camera 116 may be movable in the vertical direction. This is to accurately focus on each pad 10. However, in practice, if the pad 10 is standardized, the black and white line scanning camera 114 and the color line scanning camera 116 may be fixed at a predetermined position in the vertical direction.

3, 5, and 6, the lighting device 118 is installed between the cameras 114, 116 and the pad 10, in particular in the proximity of the pad 10. The lighting device 118 is fixed to the support 104. The lighting device 118 extends long along the moving direction axis of the pad 10. The lower side of the lighting device 118 extends inwardly with the groove along the direction of movement. The inner surface of the groove forms the reflecting surface 130. It is preferable that the reflecting surface 130 of this groove has a circular cross section. On the other hand, the upper portion of the lighting device 118 is provided with a slit 132 that is drilled in the vertical direction and extends along the movement direction axis. When the pad 10 is in the inspection position, light is incident on the cameras 114 and 116 through this slit 132.

A light emitting device 134 for a black and white line scanning camera extending in a long position is installed at a position corresponding to the black and white line scanning camera 114. The light emitting device 134 for monochrome cameras is fixed at positions adjacent to the slits 132 on both sides of the slits 132. This is to allow light to enter the pad as vertically as possible. In addition, it is good that the shadow of the grooves is not generated by the illumination. For this purpose, it is necessary to arrange the light emitting element exactly perpendicular to the valley extending in the circumferential direction. As shown in the figure, the light emitting device 134 is preferably an LED element array having a narrow width, a planar shape, and a long shape.

Likewise, the light emitting element 136 for the color line scanning camera is installed at a position corresponding to the color line scanning camera 116. As shown in the figure, the color light emitting element is preferably an arc array which covers the entire reflecting surface of the lighting device and is a long array of LED elements in the radial direction of the pad. The LED device is recommended to use a white LED to maximize the primary color of the object. Although not shown in detail, it is preferable that the light scattering diffuser plate made of transparent or translucent is mounted on the front of the color light emitting device. Of course, this diffuser plate is not installed on the path of light extending from the pad to the color line scan camera.

The lengths of the light emitting elements 134 and 136 may be larger than the pitch for moving the pad 10 for inspection. That is, the pitch is preferably shorter than the length of the light emitting element and the length that the camera can photograph at a time.

Referring back to FIG. 4, the defect inspection apparatus 100 includes a central controller 140. The central control unit 140 can be configured as a normal PC. The PC used as the central controller 140 includes a processor 142, a memory 144, and a storage device (auxiliary storage device) 146. The processor 142 may use a variety of processors, such as an Intel Pentium processor.

The central control unit computer 140 includes a first frame grabber 148 and a second frame grabber 150. The first frame grabber 148 is connected to the color line scanning camera 116. The second frame grabber 150 is connected to the black and white line scanning camera 114. Each frame grabber 148 and 150 captures an electrical signal transmitted from the cameras 114 and 116 and converts it into a digital signal. Each frame grabber 148,150 is mounted in the form of a card inserted into a slot of a PC. An example of such a frame grabber (148,150) is a product named PC-Linescan (CORECO, inc; also known as CORECO iMAGING in Korea) located in Quebec, Canada (Internet website: www.imaging.com It is available from).

The central controller 140 includes a digital input / output board 152. The digital input / output board 152 outputs a signal for driving a vacuum device for driving a vacuum suction fixture provided on the turntable, and driving signals for various relays or solenoids not shown in detail in the drawing. Also, it receives a signal transmitted from a sensor such as a limit sensor and an input signal of a button. Specifically, the digital input board is a board composed of a number of (4 to 16) relays and signal input devices. The digital input board checks the status of an on-off switch or an external switch of an external device. In addition, start, stop, emergency stop button and turntable home sensor, linear sensor limit sensor and home sensor signal input function Serves as a switch for solenoid devices for supplying vacuum and compressed air.

The central controller 140 includes a biaxial motion control unit 154. This control unit 154 is for controlling the drive drivers for driving the motors provided in the turntable 110 and the linear movement unit 112.

The display device 120 and the input device 122 are connected to the central controller 140. Meanwhile, the defect inspection apparatus 100 includes an encoder distributor 156. The encoder distributor 156 is connected to the encoder 128 provided in the turntable 110 and is also connected to each frame grabber 148 and 150. The encoder distributor 156 sends a signal to the frame grabbers 148 and 150 to capture the signal in synchronization with the rotation of the turntable 110. To do this, the encoder distributor divides the pulse generated by the motor into two and delivers it to the capture board for color and monochrome cameras.

The defect inspection apparatus 100 includes a motor driving driver 158 for driving the turntable rotary motor 126 and a motor driving driver 160 for supplying power to the driving motor 113 of the linear movement device 112. do. The driver 158 for the rotation motor of the turntable 110 supplies power to drive the motor, and controls the motor based on the encoder signal.

The storage device stores the OS and various application programs. In particular, a program for processing the acquired image information is stored. This program processes the image information obtained by driving the image data processing processor as described below to determine the presence of a defect. The data processing unit is formed in the central control unit computer 140 by the driving of this program. In the above description, the central controller 140 is implemented using a PC, but the present invention is not limited thereto. It will be understood by those skilled in the art that the image data acquisition unit, the image data processing unit, the 2-axis motion control unit, etc. of the central controller 140 may be configured as a hardware device and may be connected to each other to form a central controller implemented in hardware. will be.

Hereinafter, the process of detecting the defect of the pad 10 is demonstrated. 2, 3, and 7, the linear movement device 112 is driven to move the turntable 110 to the loading position of the pad. The pad 10 to be inspected is mounted on the turntable 110 (701). The linear movement device 112 is driven again to move the pad 10 to the inspection position (703).

First, a black and white image is acquired with a black and white line scanning camera 114. When acquiring a black-and-white image, an image of a width R / 8 (pitch) obtained by, for example, dividing the radius R of the pad 10 by eight in one rotation is obtained (the present invention is limited to eight portions). Is not). To do this, when initially setting the position 705, the position away from the outermost edge of the pad 10 by R / 16 is centered on the black and white line scanning camera 114. Power is supplied to the line LEDs in the lighting device 118 to supply light to the surface of the pad. This completes the preparation for scanning the pad surface.

Thereafter, the turntable 110 is rotated. The black and white line scanning camera 114 scans 707 the black and white image. The electrical signal of the image is transferred to the second frame grabber 150, captured, converted into a digital signal, and stored in a memory or a storage device as one frame. At this time, the rotation of the turntable 110 and the data acquisition of the second frame grabber 150 are synchronized.

After obtaining one data frame (sector), the linear movement unit 112 linearly transfers 709 the turntable 110 by one pitch (R / 8). After the transfer, the image is scanned by rotating the turntable 110 again to obtain the next data frames. By repeating the scanning operation by the linear movement of the turntable and the rotation of the turntable, the scanning of the entire pad surface 11 can be completed. Even after each transfer, the turntable 110 is rotated at different rotation speeds in order to make the scanning speed substantially the same or similar. That is, when scanning the edge side, the rotation speed (angular velocity) is slowed down, and when scanning the center side, the rotation speed is relatively high.

The color line scanning camera 116 then scans the color image to obtain data. Scanning with the color line scanning camera 116 is generally the same as scanning with the black and white line scanning camera 114. When scanning with the color line scanning camera 116, the scanning width can be made wider at one time. For example, scanning the width by half the radius, ie R / 2, at a time.

The image data obtained as described above is analyzed through a process of processing a gray scale, processing an intensity value, processing a saturation value, and processing a hue value as described below. The basic method for determining what defects for each defect is as described above. After inspection of the defect, the result is displayed on the display device.

Hereinafter, a method of detecting defects by processing data with image data will be described. First, a process of detecting particles using gray scale (also called gray level and displaying brightness of light) will be described. 8A is an image with particles. Fig. 8B shows a gray scale value from the frame data of this image along the red straight line indicated by the arrow in Fig. 8A. As can be seen from Fig. 8A, the valley portion and the particle portion are darkened and the gray scale is small. Therefore, if an appropriate gray scale is set as a threshold value and particle defects, there is a possibility that it is determined as a bone defect. As such, it is better to subtract the bone component from the gray scale because it is difficult to distinguish between the bone and the particles.

As can be seen in Figure 8b, the pad surface has a rough gray scale due to the pores. Here, the particles are difficult to distinguish clearly, eliminating the effects of pores. For this purpose, the gray scale average value of surrounding pixels is obtained for each pixel. As can be seen from Fig. 8C, which shows the average value, the influence of the pore is eliminated and the groove component is clearly seen.

The average value is obtained by averaging, for example, grayscale data obtained by rotating the turntable by a certain length or angle in the circumferential direction with respect to any dot on the radial line of the pad scanned by the monochrome line scan camera. In detail, the black and white line scan camera scans the radius into eight equal parts, and the radial unit width for scanning once consists of 2048 dots. In other words, the line crossing the unit width is composed of 2048 dots. When the pad is rotated to scan such radial lines by 512, these 512 lines of data represent one sector (also known as a frame; sectors herein refer to a bundle of lines that are processed at one time. In general, a frame is a unit that is scanned at a time by an area scan camera. In one embodiment of the present invention, a line scan camera is used, and a plurality of lines are processed rather than each line individually. Scanning lines and processing them in one batch is advantageous in terms of speed or handling, so in this embodiment, even though it is a line-by-line scan method, for example, 512 lines are processed in a group called sectors. In the specification, this is also called a frame). If the radius of the pad is divided into eight, the data of the outermost edge portion can be composed of 51 sectors obtained by one rotation. In the case of the innermost part, data obtained by one revolution may be composed of 26 sectors.

The 512 lines of one section are divided into four sections and averaged for each section. In other words, for each of 2048 dots, the average value is obtained with gray scale obtained from 128 lines. Of course, the present invention is not limited to the above-described method for obtaining the average value, and the above-described method for obtaining the average value is described by way of example.

Thereafter, the average value as shown in Fig. 8C is subtracted from the gray scale of each pixel shown in Fig. 8B. Then, as shown in Fig. 8D, the bone component is removed to obtain a leveled gray scale. In Fig. 8D, the place where the gray scale is smaller than a constant value is detected as particles.

Because the camera lens is spherical, the amount of light that passes through the lens edges decreases. Thus, under the same lighting conditions, the center of the lens is bright but gradually darkens toward the edge. As a result, it is difficult to separate particles from the lens edge. In order to solve this problem, there is a method using a large-diameter lens. However, the lens alone cannot solve the problem completely, resulting in a gray scale as shown in Fig. 9B. Fig. 9B shows the gray scale along the horizontal line indicated by the arrow in Fig. 9A. The illuminance is gradually lowered toward the right end, and the edge is almost lower than the gray scale of the particle. Therefore, if you simply classify particles with a certain threshold, the right edge is also recognized as particles.

In order to solve this problem, the average gray scale as shown in Fig. 9C is obtained in the same manner as described above. Subtracting the average value of FIG. 9C from the gray scale of each pixel shown in FIG. 9B, the illuminance difference is removed and only the particle signal remains. This eliminates the influence of illumination and can detect particles.

Detection of defects, such as spots with weak signal contrast, utilizes a color line scan camera 116. The signal of the image captured by the color line scan camera 116 is separated into RGB and HSI values (also referred to as three elements of light, indicating Hue, Saturation, and Intensity), and the separated values are recombined to amplify the image contrast. The RGB and HSI values are used to isolate defects based on the characteristics of the spot as described above.

For defects that are difficult to detect only in black and white grayscale, a new standard can be created to detect experimentally using data scanned with a color linescan camera. First, RGB values of image data obtained by scanning in the color line scan camera 116 are converted into HSI, which is three elements of light. Combining the total of six signals obtained here, we experimentally determine which of the six signals is the largest difference between the defect and the normal pad surface, and what the threshold for judging is the defect. Thereafter, the same defect can be determined immediately by the signal value to be compared among the six signals. This is the method that can be applied when a new kind of defect is found. The value to be compared can be defined by, for example, Level = I * f _i -S * f _s (f _i : intensity coefficient, f _s : saturation coefficient). The difference between the normal pad surface at this defined level value is the determination of a defect.

On the other hand, the central control unit 140 may find a defect through the above process, and may perform statistical processing by distinguishing the image of the defect by its size and type. By performing this statistical process, the user can identify the tendency of the polishing pad in the short term or the long term, the association with the process, the association with the yield, and the like.

The defect inspection apparatus 100 of the present invention may further include a camera capable of capturing an image. In this case, it is convenient to be able to check the defect found in the device by image.

In the above embodiment, the turntable is rotated and scanned. Alternatively, the turntable may be scanned using an X-Y table.

According to the configuration of the present invention, by inspecting the pad defect, there is an advantage that can block in advance the process defects that can be caused by the pad, find the cause of the defect already occurred and obtain a direction for further process improvement. In addition, the present invention, after the detection of the defect by distinguishing the image by the image and its size and type of the defect statistical processing, the user can identify the tendency of the polishing pad in the short or long term, the association with the process, the correlation with the yield, etc. Can be identified.

By using a turntable, the signal impact of the pad goal can be minimized. The structure of the apparatus is simple by making the structure for moving the pad into a turntable structure. The turntable structure requires only relatively small spaces to transport the pads. By rotating the pad in a turntable manner, the direction of rotation of the illumination and the direction of rotation are perpendicular, and the line CCD of the camera is also arranged vertically, thereby minimizing signal contrast between the valley and the pad surface. By using a camera equipped with a color line CCD, inherent defects such as spots with low contrast are reliably found.

Claims (22)

In order to detect defects generated in a polishing pad for chemically and mechanically polishing a wafer, A pad driving device for mounting and moving the pad, A camera installed toward the pad and outputting an image of the pad as an electric signal; A digital image data acquisition device for converting an electrical signal transmitted from the camera into a digital signal; An image data processing unit which processes the image data transferred from the digital image data acquisition device to detect a defect, The image data processing unit obtains one or two or more values of quantitative characteristic values of light obtained from the image data for any one point of the image data of the pad obtained by the image data obtaining apparatus, and obtains the obtained quantitative characteristic. When a level value obtained from any one or a combination of two or more values differs by more than a predetermined amount from a level value obtained from image data around the point of the pad, the point at which the difference appears is recognized as a defect. The defect detection apparatus of the polishing pad. The apparatus of claim 1, wherein the camera is a line scan camera having a black and white or color line CCD extending radially. According to claim 2, wherein the pad drive device has a turntable for rotating the center of the pad around the center axis, And a longitudinal direction of the line CCD of the line camera coincides with a radial direction of the pad. The apparatus for detecting a defect of a polishing pad according to claim 1, further comprising a lighting device facing the surface of the pad. According to claim 3, further comprising a lighting device installed between the camera and the pad, The lighting apparatus includes a support having a slit extending in a radial direction of the pad, and a light emitting device extending along the slit and installed toward the pad around the slit. . The LED array of a long white light source according to claim 5, wherein the support is formed with a groove having a semicircular cross section around the slit, and the light emitting device has an arc cross section so as to cover at least a portion of the surface of the groove. Defect detection device of the polishing pad comprising a. The apparatus of claim 5, wherein the support is formed with a groove having a semicircular cross section around the slit, and the light emitting device is installed adjacent to the slit along at least a longitudinal portion of the groove surface and has a generally narrow width. The apparatus for detecting a defect of a polishing pad comprising an LED array. delete The image data processing unit of claim 1, wherein the image data processing unit calculates an average value of the level values for points at adjacent positions of the point in processing data of the one point on a pad, And the average level value is subtracted from the level value of the polishing pad. 10. The apparatus of claim 9, wherein points at adjacent positions selected to obtain the average value in the image data processing unit are located on a line extending from the one point (point to be processed) along the conveying direction. The defect detection apparatus of the polishing pad characterized by the above-mentioned. The apparatus of claim 1, wherein the light quantitative characteristic value of the image data processed by the image data processing unit is an HSI value. The apparatus of claim 1, wherein the pad driving device includes a turntable configured to rotate the center of the pad as a center axis, wherein the pad driving device includes a pulse signal corresponding to a rotation of a predetermined angle of the turntable and a trigger signal of the image data acquisition device. The defect detection apparatus of the polishing pad which synchronized the same. The apparatus of claim 12, wherein the turntable includes a stepping motor for rotation, and the pulse signal corresponding to the rotation is a stepping pulse signal of the stepping motor. The apparatus of claim 12, wherein the turntable includes a rotary encoder and an encoder distributor connected to the rotary encoder, and the encoder distributor is connected to the image data acquisition device to transmit the pulse signal. . In order to detect defects generated in a polishing pad for chemically and mechanically polishing a wafer, Rotating the polishing pad about its center; Acquiring a linear image extending radially of the polishing pad on the polishing pad; Converting the image into an electrical signal; Converting the electrical signal into digital image data; Processing the digital image data, The processing of the digital image data may include obtaining one or more values of quantitative characteristic values of light obtained from image data for any one point of the image data of the polishing pad, and among the obtained quantitative characteristic values. When a level value obtained from any one or a combination of two or more appears a difference more than a predetermined amount from a level value obtained from image data around the point of the polishing pad, the point at which the difference appears is recognized as a defect. A defect detection method of a polishing pad. delete 16. The method of claim 15, wherein the processing of the digital image data comprises obtaining an average value of the level values for points at adjacent locations of the point in processing the data of the one point on a pad. And subtracting the average level value from the level value for the point of. 18. The method of claim 17, wherein the points at adjacent positions selected to obtain the average value in the processing of the digital image data extend from the one point (point to be processed) along the conveying direction. A defect detection method of a polishing pad, characterized in that located on the line. The method of claim 15, wherein the quantitative characteristic value of light of the image data processed in the processing of the digital image data is an HSI value. 20. The method of claim 19, wherein the level value L = I * f _i -S * f _s (I: intensity value, f _i : coefficient of intensity, S: saturation value, f _s : coefficient of saturation) A defect detection method of a polishing pad. The apparatus of claim 1, wherein the data processing unit includes an image data processing processor and a storage device, and the storage device stores a program for driving the image data processing processor. A program executed by an image data processing processor included in the apparatus of claim 21, the method comprising: obtaining one or two or more values of quantitative characteristic values of light obtained from image data for any one point of image data of a polishing pad; A program for calculating a difference between the level values obtained from any one or a combination of two or more of the obtained quantitative characteristic values obtained from the image data around the point of the polishing pad, and comparing whether the difference is a difference more than a predetermined amount. Computer-readable recording medium.